diff --git a/ofborg/src/tasks/eval/nixpkgs.rs b/ofborg/src/tasks/eval/nixpkgs.rs
index 1170953..7e3b23c 100644
--- a/ofborg/src/tasks/eval/nixpkgs.rs
+++ b/ofborg/src/tasks/eval/nixpkgs.rs
@@ -4,17 +4,23 @@ use ofborg::commitstatus::CommitStatus;
 use ofborg::evalchecker::EvalChecker;
 use ofborg::message::buildjob::BuildJob;
 use ofborg::nix::Nix;
-use ofborg::tasks::eval::{EvaluationStrategy, StepResult};
+use ofborg::tagger::StdenvTagger;
+use ofborg::tasks::eval::{stdenvs::Stdenvs, EvaluationStrategy, StepResult};
 use ofborg::tasks::evaluate::update_labels;
 use std::path::Path;
 
 pub struct NixpkgsStrategy<'a> {
     issue_ref: &'a IssueRef<'a>,
     nix: Nix,
+    stdenv_diff: Option<Stdenvs>,
 }
 impl<'a> NixpkgsStrategy<'a> {
     pub fn new(issue_ref: &'a IssueRef, nix: Nix) -> NixpkgsStrategy<'a> {
-        Self { issue_ref, nix }
+        Self {
+            issue_ref,
+            nix,
+            stdenv_diff: None,
+        }
     }
 
     fn tag_from_title(&self) {
@@ -31,6 +37,32 @@ impl<'a> NixpkgsStrategy<'a> {
             update_labels(&self.issue_ref, &[String::from("6.topic: darwin")], &[]);
         }
     }
+
+    fn check_stdenvs_before(&mut self, dir: &Path) {
+        let mut stdenvs = Stdenvs::new(self.nix.clone(), dir.to_path_buf());
+        stdenvs.identify_before();
+        self.stdenv_diff = Some(stdenvs);
+    }
+
+    fn check_stdenvs_after(&mut self) {
+        if let Some(ref mut stdenvs) = self.stdenv_diff {
+            stdenvs.identify_after();
+        }
+    }
+
+    fn update_stdenv_labels(&self) {
+        if let Some(ref stdenvs) = self.stdenv_diff {
+            let mut stdenvtagger = StdenvTagger::new();
+            if !stdenvs.are_same() {
+                stdenvtagger.changed(stdenvs.changed());
+            }
+            update_labels(
+                &self.issue_ref,
+                &stdenvtagger.tags_to_add(),
+                &stdenvtagger.tags_to_remove(),
+            );
+        }
+    }
 }
 
 impl<'a> EvaluationStrategy for NixpkgsStrategy<'a> {
@@ -39,7 +71,13 @@ impl<'a> EvaluationStrategy for NixpkgsStrategy<'a> {
         Ok(())
     }
 
-    fn on_target_branch(&mut self, _co: &Path, _status: &mut CommitStatus) -> StepResult<()> {
+    fn on_target_branch(&mut self, dir: &Path, status: &mut CommitStatus) -> StepResult<()> {
+        status.set_with_description(
+            "Checking original stdenvs",
+            hubcaps::statuses::State::Pending,
+        );
+        self.check_stdenvs_before(dir);
+
         Ok(())
     }
 
@@ -49,7 +87,10 @@ impl<'a> EvaluationStrategy for NixpkgsStrategy<'a> {
 
     fn merge_conflict(&mut self) {}
 
-    fn after_merge(&mut self, _status: &mut CommitStatus) -> StepResult<()> {
+    fn after_merge(&mut self, status: &mut CommitStatus) -> StepResult<()> {
+        status.set_with_description("Checking new stdenvs", hubcaps::statuses::State::Pending);
+        self.check_stdenvs_after();
+
         Ok(())
     }
 
@@ -62,6 +103,8 @@ impl<'a> EvaluationStrategy for NixpkgsStrategy<'a> {
         _co: &Path,
         _status: &mut CommitStatus,
     ) -> StepResult<Vec<BuildJob>> {
+        self.update_stdenv_labels();
+
         Ok(vec![])
     }
 }
diff --git a/ofborg/src/tasks/evaluate.rs b/ofborg/src/tasks/evaluate.rs
index 91ddb7d..da2c151 100644
--- a/ofborg/src/tasks/evaluate.rs
+++ b/ofborg/src/tasks/evaluate.rs
@@ -21,9 +21,7 @@ use ofborg::outpathdiff::{OutPathDiff, OutPaths};
 use ofborg::stats;
 use ofborg::stats::Event;
 use ofborg::systems;
-use ofborg::tagger::{
-    MaintainerPRTagger, PathsTagger, PkgsAddedRemovedTagger, RebuildTagger, StdenvTagger,
-};
+use ofborg::tagger::{MaintainerPRTagger, PathsTagger, PkgsAddedRemovedTagger, RebuildTagger};
 use ofborg::worker;
 use std::collections::HashMap;
 use std::path::Path;
@@ -222,14 +220,6 @@ impl<E: stats::SysEvents + 'static> worker::SimpleWorker for EvaluationWorker<E>
             return self.actions().skip(&job);
         }
 
-        overall_status.set_with_description(
-            "Checking original stdenvs",
-            hubcaps::statuses::State::Pending,
-        );
-
-        let mut stdenvs = eval::Stdenvs::new(self.nix.clone(), PathBuf::from(&refpath));
-        stdenvs.identify_before();
-
         let mut rebuildsniff = OutPathDiff::new(self.nix.clone(), PathBuf::from(&refpath));
 
         overall_status.set_with_description(
@@ -311,11 +301,6 @@ impl<E: stats::SysEvents + 'static> worker::SimpleWorker for EvaluationWorker<E>
             return self.actions().skip(&job);
         }
 
-        overall_status
-            .set_with_description("Checking new stdenvs", hubcaps::statuses::State::Pending);
-
-        stdenvs.identify_after();
-
         overall_status
             .set_with_description("Checking new out paths", hubcaps::statuses::State::Pending);
 
@@ -552,16 +537,6 @@ impl<E: stats::SysEvents + 'static> worker::SimpleWorker for EvaluationWorker<E>
                 hubcaps::statuses::State::Pending,
             );
 
-            let mut stdenvtagger = StdenvTagger::new();
-            if !stdenvs.are_same() {
-                stdenvtagger.changed(stdenvs.changed());
-            }
-            update_labels(
-                &issue_ref,
-                &stdenvtagger.tags_to_add(),
-                &stdenvtagger.tags_to_remove(),
-            );
-
             if let Some((removed, added)) = rebuildsniff.package_diff() {
                 let mut addremovetagger = PkgsAddedRemovedTagger::new();
                 addremovetagger.changed(&removed, &added);